Pluggable optical optic system having a lens fiber stop

ABSTRACT

An optical coupler having two refractive lenses for coupling an optoelectronic element and an optical medium to each other. One lens may be in contact with the optical medium. The refractive index of the one lens may be similar to the index of the optical medium. The optoelectronic element may be a light source or a detector. The light source may be a laser. The lenses may be glass ball lenses. One of the ball lenses may be a half ball lens. If the optical medium is an optical fiber, one of the lenses may a fiber stop for the fiber when inserted in a receptacle of the coupler.

BACKGROUND

[0001] The invention relates to optical couplers and particularly tosuch devices that couple optoelectronic elements and optical fiber. Moreparticularly, the invention relates to couplers having lenses.

[0002] Several patent documents may be related to optical couplingbetween optoelectronic elements and optical media. They include U.S.Pat. No. 6,086,263 by Selli et al., issued Jul. 11, 2000, entitled“Active Device Receptacle” and owned by the assignee of the presentapplication; U.S. Pat. No. 6,302,596 B1 by Cohen et al., issued Oct. 16,2001, and entitled “Small Form Factor Optoelectronic Receivers”; U.S.Pat. No. 5,692,083 by Bennet, issued Nov. 25, 1997, and entitled“In-Line Unitary Optical Device Mount and Package therefore”; and U.S.Pat. No. 6,536,959 B2, by Kuhn et al., issued Mar. 25, 2003, andentitled “Coupling Configuration for Connecting an Optical Fiber to anOptoelectronic Component”; which are herein incorporated by reference.

[0003] In the context of the invention, the optoelectronic element maybe understood as being a transmitter or a receiver. When electricallydriven, the optoelectronic element in the form of a transmitter or lightsource converts the electrical signals into optical signals that aretransmitted as light signals. On receiving optical signals, theoptoelectronic element in the form of a receiver or detector convertsthese signals into corresponding electrical signals that can be tappedoff at the output. In addition, an optical fiber may be understood to beany apparatus for forwarding an optical signal with spatial limitation,in particular preformed optical fibers and so-called waveguides.

[0004] A problem with couplers may involve light reflected back to thelight source. This may be an issue because, for instance, some fiberoptic transmitters suffer from undesirable and performance degradingreflections from the face end of the optical fiber back into the coupledoptoelectronic element device (e.g., a semiconductor laser). Here, thefiber's surface and facing surface of the optoelectronic element deviceform a Fabry-Perot cavity which may modulate the light from the lasertransmitter or semiconductor laser and consequently produce unwantedfluctuations in the power coupled to the optical fiber. Further, theoptical energy reflected directly into the laser cavity may causeadditional noise in the laser's output. For these reasons, it would bedesirable to reduce and minimize the return reflections from the fiberface in the coupler.

SUMMARY

[0005] The invention is an optical coupler which may couple a lightsource or detector and optical fiber to each other. The coupler may havea fiber stop which is a lens. That is, the optical fiber may have an endthat is in contact with a lens of the coupler.

BRIEF DESCRIPTION OF THE DRAWING

[0006]FIG. 1 is an optical diagram of a two ball lens coupler having anair gap between the optical fiber end and the nearest lens.

[0007]FIG. 2 is a diagram of a two ball lens coupler having a fiber stoplens.

[0008]FIG. 3 is a diagram of a one and a half lens couple having a flatlens surface as a fiber stop.

[0009]FIG. 4 is a side sectional view of a two-ball lens couplerapparatus implementing the coupler of FIG. 1;

[0010]FIG. 5 is a side sectional view of a two-ball lens couplerapparatus implementing the coupler of FIG. 2;

[0011]FIG. 6 is a side sectional view of a one and a half ball lenscoupler implementing the coupler of FIG. 3; and

[0012]FIGS. 7a, 7 b and 7 c are a side view and perspective views,respectively, of the coupler housing hardware.

DESCRIPTION

[0013]FIG. 1 shows an optical layout of a two-ball lens optical coupler30. This two-ball lens system may be arranged to focus the light at apoint outside the second ball lens 29, possibly often with light 14nearly perfectly collimated between ball lenses 28 and 29. Light 14 maybe emitted by a light source 11. Source 11 may be a laser such as avertical cavity surface emitting laser. Light 14 may propagate throughball lens 28 and 29. Light 14 may be focused by lens 28 and 29 on endface 22 of core 23 of optical fiber 33. Light 14 may propagate from balllens 29 through air onto the end of core 23. The Fresnel coefficient ofback reflectance 31 of light 14 for coupler 30 may be determined withthe following formula, where “n” is an index of refraction of light ofthe subject material,

((n_(lens glass)−n_(air))/(n_(lens glass)+n_(air)))².

[0014] Calculation of reflected light 31 may amount to about 4 percentof the originally emitted light 14 for an n_(lens glass)=1.5 andn_(air)=1.0. This amount of back reflectance light 31 is significantenough to cause unwanted fluctuations in power of light 14 from source11 coupled to core 23 of optical fiber 33 at end face 22 and additionalnoise in light 14 at the output of light source 11.

[0015]FIG. 2 shows an optical layout of a two-ball optical coupler 10.Light 14 may be emanated by source 11. Light 14 may propagate throughball lens 15 and into ball lens 16, respectively. Ball lens 16 may focuslight 14 down to a spot at or near the surface of lens 16 where light 14may exit lens 16. Core 23 of fiber 33 may have end face 22 that issituated against the surface of ball lens 16 at that spot where the raysof light 14 converge together. This arrangement may minimize reflectanceof light 14 into light 32 that moves towards the direction of lightsource 11. One cause of reflected light 32 may be at end face 22 offiber core 23 being coupled. A reduction of reflectance light 32 mayresult from having end face 22 of core 23 of fiber 33 of coupler 10physically in contact with a lens, such as ball lens 16. The reductionof reflected light 32 may occur because an air interface between lens 16and fiber end 22 is eliminated at the point of contact. The Fresnelcoefficient of back reflectance 32 of light 14, in view of coupler 10,may be determined with the following formula,

((n_(lens glass)—n_(glass fiber))/(n_(lens glass)+n_(glass fiber)))².

[0016] Calculation of reflected light 32 may amount to about 0.01percent of light 14 for an n_(glass fiber)=1.47 and n_(lens glass)=1.5.This calculated amount of reflected light 32 in coupler 10 is about 0.25percent of the calculated reflected light 31 in coupler 30.

[0017]FIG. 3 shows an optical layout of a one and a half-ball opticalcoupler 20. Light 14 may be emitted by light source 11. Light 14 maypropagate through ball lens 25 and into a half-ball lens 26. Half-balllens 26 may focus light 14 down to a spot at or near the flat surface oflens 26 where light 14 may exit lens 26. Core 23 of fiber 33 may have anend 22 that is situated against the flat surface of ball lens 26 at thatspot where the rays of light 14 converge together. This arrangement mayminimize reflectance of light 14 as light 34 propagating towards thedirection of light source 11. One cause of reflection may be at end face22 of fiber core 23 being coupled. A reduction of reflectance light 34may result from having end face 22 of core 23 of fiber 33 of coupler 10physically in contact with half-ball lens 26. The reduction of reflectedlight 34 may occur because the air interface between lens 26 and fiberend 22 is eliminated with the point of contact. The Fresnel coefficientof back reflectance 34 of light 14, in view of coupler 20, may bedetermined with the following applicable formula,

((n_(lens glass)−n_(glass fiber))/(n_(lens glass)+n_(glass fiber)))².

[0018] Calculation of reflected light 34 may amount to about 0.01percent of light 14 for an n_(glass fiber)=1.47 and n_(lens glass)=1.5.This calculated amount of reflected light 34 in coupler 20 is about 0.25percent of the calculated reflected light 31 in coupler 30. Thecloseness of the indices of refraction of the glass fiber and lens glassappears to result in a minimizing of light reflected from the fiber coreend face. The composition of ball lenses 15, 16, 25, 26, 28 and 29 mayinclude BK7™ glass or like material.

[0019] The following table indicates the amount of reflected light whichis indicated in terms of a percentage of light to the end of the opticalmedium such as a fiber end face relative to the indices of refraction ofthe lens proximate to the optical medium and of the optical medium. Theformula used for the table is

((n_(lens glass)−n_(medium))/(n_(lens glass)+n_(medium)))².

[0020] n_(lens glass) n_(medium) % of Reflected Light 1.50 1.00 4.001.50 1.10 2.37 1.50 1.20 1.23 1.50 1.30 0.510 1.50 1.35 0.277 1.50 1.400.119 1.50 1.41 0.0957 1.50 1.42 0.0751 1.50 1.425 0.0657 1.50 1.430.0571 1.50 1.44 0.0416 1.50 1.45 0.0287 1.50 1.46 0.0183 1.50 1.470.0120 1.50 1.48 0.00450 1.50 1.49 0.00112

[0021] If the medium has an index of refraction 10 percent lower thanthat of the lens, the light reflected is about 0.277 percent of thelight going to the medium, which is about 7 percent of light reflectedwith air as an intervening medium between the lens and the opticalmedium. If the medium has an index of refraction 5 percent lower thanthat of the lens, the light reflected is about 0.0657 percent of thelight going to the medium, which is about 1.6 percent of light reflectedwith air as an intervening medium between the lens and the opticalmedium. In the table, the medium may be the intervening medium. However,if there is contact between the lens and the optical medium thecalculation may apply to the index of refraction of the optical medium.Hence, while this discussion has shown that the optimum implementationof this invention includes matching the fiber stop optical element'sindex of refraction to that of the fiber, significant practicalperformance gain (i.e., reduction of reflectance feedback) isaccomplished even in imperfectly index matched implementations.

[0022]FIG. 4 shows an example of coupler 30. This coupler may be a twoball lens system having an optical fiber 33 interface with a space 35between the nearest ball lens 29 and fiber face 22. Space 35 may be avacuum or filled with air or other optical medium material. Coupler 30may have a laser light source 11, such as a vertical cavity surfaceemitting laser (VCSEL). Source 11 may be contained in a hermeticallysealed package 12 having a window 13. Source 11 may emit light 14through window 13, ball lenses 28 and 29. Lenses 28 and 29 may bestructurally supported by an optical subassembly housing 17. Housing 17may be structurally supported by fiber optic coupler barrel 18. Package12 may be situated in a z-alignment sleeve 19. Package 12, for example,may be a TO-56 can. Barrel 18 and sleeve 19 may be fabricated from astainless metal alloy. The materials of these components, includinghousing 17, may be thermally matched. Housing 17 may be of a ceramicsuch as zirconia or of a metal. Sleeve 19 may be fit into barrel 18 andslide back and forth in order to adjust the distance of source 11 fromball lens 28.

[0023] After the accomplishment of distance adjustment between source 11and lens 28, then sleeve 19 may be fixed or secured to barrel 18 with aweld spot, pressed fit, glue, or the like. A ferrule 24 having anoptical fiber 33 in it may be inserted into opening 21. An end face 22of fiber 33 may be at a certain distance from ball lens 29, with air oranother medium between end face 22 and ball lens 29. The other mediumbetween end face 22 and ball lens 29 may be a light transmitting opticalmedium having a preferred index of refraction. The index of refractionmay match the index of fiber core 23 or lens 29, or both of the latter.The distances of the ball lens 29 from fiber end face 22 and ball lens28 and of ball lens 28 from light source 11 may be adjusted for anotheroptical medium between ball lens 29 and end face 22.

[0024] Couplers 10, 20 and 30 may be designed to operate at 850 nm, 1310nm or 1550 nm. They may instead be designed for some other wavelength.These couplers may be designed in various configurations such as withone lens, molded lens or lenses, or more than two lenses.

[0025]FIG. 5 shows an illustrative implementation of coupler 10. Thestructure of coupler 10 may be similar to that of coupler 30 except thatball lens 16, which is the lens closest to fiber end face 22, may be afiber stop for fiber 33 and its core 23. Coupler 10 may have a lensarrangement, which includes a ball lens 15 near source 11, has the lightfocused at or slightly inside the second ball lens 16 surface so thatthe source 11 to fiber 33 ray path may be much different than that ofcoupler 30. Fiber 33 being coupled to may be arranged in such a mannerthat it is in physical contact with the surface of the second ball lens16. The components of coupler 10 may be held in place by an externalhousing fabricated in such a manner that the laser diode, opticalelements and receiving optical fiber cable are held in the correctpositions to effect the above-noted focusing.

[0026]FIG. 6 shows an illustrative implementation of coupler 20. System20 may involve a use of a half-ball lens 26 in the system. In this twoelement full ball-half ball design, the fiber-to-lens contact is thusplanar instead of a single point of contact as in the two-ball lensapproach of system 10. The half-ball lens configuration may have theadvantages of loosened radial alignment tolerances and reduced contactpressure which may make fiber end face 22 and fiber stop lens 26 lessprone to wear or potential surface damage upon repeated insertions offerrule 24. Ferrule 24 may be fabricated from a ceramic such as zirconiaor form another material. End face 22 of core 23 may be a polished roundsurfaced tip having a relatively large radius or be flat. There may be aball lens 25 between lens 26 and source 11. Fiber 33 may be single modebut could be multi-mode as desired. Likewise, light source 11 may besingle mode but could be multi-mode.

[0027]FIG. 7a shows an external side view of couplers 10, 20 and 30,without ferrule 24 inserted, shown in FIGS. 4-6. FIGS. 7b and 7 c areperspective views of these couplers.

[0028] A multitude of the optical couplers may be incorporated in anarray-arrangement. Such arrangement may be of a one or two dimensionallayout.

[0029] Although the invention has been described with respect to atleast one illustrative embodiment, many variations and modifications,including aspheric lens variations, modifications and substitutions,will become apparent to those skilled in the art upon reading thepresent specification. It is therefore the intention that the appendedclaims be interpreted as broadly as possible in view of the prior art toinclude all such variations and modifications.

What is claimed is:
 1. An optical coupler comprising: a first structure;an optoelectronic element attached to said first structure; a first balllens supported by said first structure; a second ball lens supported bysaid first structure; and a receptacle for a ferrule having an opticalmedium attached to said first structure.
 2. The coupler of claim 1,wherein: the optical medium is an optical fiber; and the second balllens is a fiber stop.
 3. The coupler of claim 2, wherein saidoptoelectronic element is a light source.
 4. The coupler of claim 3,wherein said optoelectronic element is a laser.
 5. The coupler of claim4, wherein said laser is a vertical cavity surface emitting laser. 6.The coupler of claim 5, wherein the optical fiber is a single modefiber.
 7. The coupler of claim 5, wherein the optical fiber is amulti-mode fiber.
 8. The coupler of claim 2, wherein the optoelectronicelement is a detector.
 9. An optical coupler comprising: a first lens; asecond lens proximate to said first lens; a first receptacle proximateto said first lens; and a second receptacle proximate to said secondlens.
 10. The coupler of claim 9, wherein: said first lens is a balllens; said second lens is a ball lens; said first receptacle is for anoptical medium connection; and said second receptacle is for anoptoelectronic element connection.
 11. The coupler of claim 10, wherein:the optical medium is an optical fiber; and said first lens is a fiberstop.
 12. The coupler of claim 9, wherein: said first lens is ahalf-ball lens; said second lens is a ball lens; said first receptacleis for an optical medium connection; and said second receptacle is foran optoelectronic element connection.
 13. The coupler of claim 12,wherein: the optical medium is an optical fiber; and said first lens isa fiber stop.
 14. Means for optical coupling comprising: first means forrefracting light from a means for providing light; and second means forrefracting light from said first means for refracting light to a meansfor conveying light; and wherein a path of light from said second meansfor refracting light to the means for conveying light is direct fromsaid second means for refracting light to said means for conveying lightthrough a point of contact between said second means for reflectinglight and said means for conveying light.
 15. The means for opticalcoupling of claim 14, wherein said point of contact in the path of lightis physical contact between said second means for refracting light andsaid means for conveying light.
 16. The means for coupling light ofclaim 15, wherein said second means for refracting light effectivelyconverges light at the point of contact.
 17. The means for couplinglight of claim 15, wherein: the means for providing light is singlemode; and the means for conveying light is single mode.
 18. The meansfor coupling light of claim 15, wherein: the means for providing lightis multi-mode; and the means for conveying light is multi-mode.
 19. Amethod for coupling light comprising: refracting light from a lightsource; refracting the refracted light to an optical medium; and whereinthe refracting the refracted light to an optical medium is performedthrough a refracting medium that is in contact with the optical medium.20. The method of claim 19, wherein the index of refraction of theoptical medium and the index of refraction of the refracting medium areapproximately the same.
 21. The method of claim 19, wherein the index ofrefraction of the optical medium is within about ten percent of theindex of refraction of the refracting medium.
 22. The method of claim21, wherein the index of refraction of the optical medium is withinabout five percent of the index of refraction of the refracting medium.23. An optical coupler comprising: a first refractive element; a secondrefractive element proximate to said first refractive element; and areceptacle proximate to said second refractive element; and wherein saidreceptacle is for receiving an optical medium that may be in contactwith said second refractive element.
 24. The coupler of claim 23,wherein said first refractive element is proximate to an optoelectronicelement.
 25. The coupler of claim 24, wherein the optoelectronic elementis a detector.
 26. The coupler of claim 24, wherein: said firstrefractive element is a first ball lens; and said second refractiveelement is a second ball lens.
 27. The coupler of claim 26, wherein: theoptical medium is an optical fiber; and the second ball lens is a fiberstop upon receipt of an optical fiber in said receptacle.
 28. Thecoupler of claim 27, wherein the optoelectronic element is a lightsource.
 29. The coupler of claim 28, wherein said light source is avertical cavity surface emitting laser.
 30. The coupler of claim 24,wherein: said first refractive element is a ball lens; and said secondrefractive element is a half ball lens.
 31. The coupler of claim 30,wherein: the optical medium is an optical fiber; and the half ball lenshas an approximately flat surface that is a fiber stop upon receipt ofan optical fiber in said receptacle.
 32. The coupler of claim 31,wherein the half ball lens has a refractive index that is within aboutten percent of the refractive index of the optical fiber.